The present invention relates to a magnetic fluid pump for transporting a fluid and a method for transporting a fluid using the same. More particularly it relates to a magnetic fluid pump which prevents the generation of particles. One use of this invention is described as intaking and discharging a resist solution during the manufacture of a semiconductor device, and a method for transporting a resist solution using the same.
In the process of manufacturing a semiconductor device, small regions of a circuit on a silicon substrate are interconnected with precisely controlled impurities doped thereinto. A resist material is coated on the semiconductor substrate to form a resist film, and the resist film is selectively exposed to an optical source such as an ultraviolet ray, an electronic ray, or an X-ray source. Then, a resist pattern is formed by developing the exposed resist film. The resist pattern remaining after development protects the substrate region which it covers during the various kinds of additive (e.g. lift-off) or subtractive (e.g. etching) processes which are performed on the resist-removed portion of the substrate, thereby affecting the exposed surface of the semiconductor substrate.
Photoresist processing has been automated since the early stages of integrated circuit technology because of the need to form small patterns on a semiconductor wafer. The more recent VLSI processing techniques require the formation of faultless, high-precision small patterns. Specifically, in photoresist processing, it is desirable to automate the process environment because this process is very sensitive to contamination by particles (e.g., hair, etc.). Semiconductor device companies have expended much effort in the development of automated facilities for the various processes, including the photoresist process.
For the coating stage of the photoresist process, a spin-coating method is generally used. The spin-coating method usually comprises securing a semiconductor wafer from the back with a vacuum chuck, and then rotating the wafer at a regular speed while a photoresist solution is dropped onto its surface.
With the development of a wafer stepper, a positive resist which has good resolution is used, but it necessitates higher quality control than previously required. Especially since the positive resist includes various solvent ingredients and polymers, the viscosity changes if it is exposed to air. Therefore, it is more difficult to maintain a uniform film thickness.
In a conventional process for resist coating using a resist coating apparatus, a resist solution in a resist container is syphoned through a hose using a pump, and then transported to the pump through a filter. Thereafter, the resist solution is transported via another hose to be dispensed (or sprayed) through a resist nozzle at the end of the hose onto the semiconductor wafer which is being spun by a rotating chuck. An automatic valve is installed between the pump and the nozzle, thereby automatically regulating the dispensed amount of resist solution.
In the conventional resist coating apparatus, a resist is coated onto a wafer after passing through a pump which is generally a bellows-type pump.
FIG. 1 and FIG. 2 are sectional views showing the operation of the conventional bellows-type pump.
FIG. 1 shows the inletting operation of the conventional bellows-type pump. A conventional bellows-type pump shown in FIGS. 1 and 2 includes a fluid inlet-side frame 4 and a fluid outlet-side frame 9. Fluid inlet-side frame 4 is connected with an inlet pipe 7 and provided with a fluid inlet valve 2. Fluid outlet-side frame 9 is connected with an outlet pipe 6 and provided with a fluid outlet valve 3. Between the pump frames 4 and 9, there is a bellows 1 which interconnects these two frames 4 and 9. FIG. 1 shows that when the bellows 1 is extended, a resist solution 10 is introduced into the pump. The fluid inlet-side frame 4 moves in the direction of the inlet pipe 7 in order to extend the bellows 1. Then, the inlet valve 2 opens and a resist solution 10 enters into the pump through the inlet pipe 7 and fluid inlet valve 2. When this happens, the fluid outlet value 3 is closed by the reduced pressure within the bellows 1.
FIG. 2 shows the operation of outletting resist solution 10, with the conventional bellows-type pump, by closing the bellows 1. When the fluid inlet-side frame 4 is moved toward the fluid outlet-side frame 9, the bellows interior volume is reduced. While the fluid inlet valve 2 is closed and the fluid output valve 3 is open, the resist solution 10 inside the bellows pump exits through the outlet pipe 6.
When the resist coating process is performed by the use of a conventional bellows-type pump, some of the impurities or molecules in the resist solution 10 crystalize, thereby forming particles which accumulate in the recessed portions of the bellows 1. Reference numeral 8 of FIGS. 1 and 2 indicate particles formed by the crystallization of the molecules or impurities of the resist solution which remain in the bellows pump. Over time, the particles 8 mix with the resist solution and exit the pump, thereby contaminating the resist. The resist solution which is then sprayed on the wafer includes particles having a size between hundreds microns and a few microns. These particles degrade the uniformity of the thickness of the resist layer which is formed on the wafer or cause a resist pattern to have a poor profile by acting as impurities in the resist layer in a later exposure or development process.
Additionally, the conventional bellows-type pump is operated by a mechanical movement which becomes unstable over time, and therefore needs to be replaced at regular intervals.